The present invention relates to an emulsifying unit, particularly for emulsifying and heating air and milk by means of steam to prepare cappuccino and the like.
Preparing cappuccino and the like usually requires emulsifying the milk; for this purpose, the operator injects in a container of cold milk a jet of steam which is generally provided by a machine for making espresso coffee.
A certain skill is required to perform this operation so as to include in the emulsion a correct amount of air, to obtain the froth that is typical of a cappuccino in the desired consistency.
The above mentioned difficulties become even greater in the case of machines for home use, wherein the amount of steam that is produced instantaneously is normally smaller.
In order to solve the above problem, U.S. Pat. No. 4,715,274 disclosed an emulsifying unit having substantially an intake chamber into which a jet of steam is fed; a milk aspiration duct and an air aspiration duct or port end in the aspiration chamber.
Another embodiment, also disclosed in the same patent, provides for a solution wherein the jet of steam passes through an aspiration duct connected to a milk aspiration port in a first portion and to an air aspiration port in a second portion.
Both of the above mentioned solutions, despite being valid from a theoretical point of view, have severe problems in practical execution since, in order to obtain a froth having the desired consistency, it is necessary to give the air aspiration hole an extremely small size; depending on the amount of steam and milk that can be fed, the hole in fact must normally have a cross-section of a few tenths of a millimeter.
It is therefore extremely difficult to provide a gauged hole of such size and also achieve the desired precision, since even a minimal error in the size of the hole leads to a significant variation in the characteristics of the product being obtained.
Another severe drawback is constituted by the fact that the air aspiration hole is provided in the region where steam and milk flow together; therefore, in the presence of heat, films of milk form relatively easily and obstruct said hole, thus substantially modifying the air inlet cross-section.
Another problem is furthermore constituted by the fact that this arrangement entails considerable difficulties in cleaning the hole correctly.